1. Field of the Invention
The present invention relates to a method of manufacturing printed circuit boards.
2. Description of the Prior Art
Conventional printed circuit boards at least one circuit layer formed on a resin board. As the miniaturization of electronic system progresses, however, the growing density of components mounted on the printed circuit board increases the heat generated from these mounted components one big problem to be solved is the deteriorating performance of these mounted components that derives from a higher temperature in the adjacent area of the printed circuit board as a result of an insufficient heat releasing capacity of these printed circuit resin boards. To cope with this, components provided with radiation fins had been mounted, but a drawback in this case was a higher cost of mounted components. As the number of mounted components increases, the printed circuit board becomes cambered due to a lesser flexural rigidity of the printed circuit resin board, which makes it impossible to be incorporated into the electronic system. Even if it could be incorporated, it comes in contact with neighboring printed circuit boards and occassionally seriously jeopardizes the circuit function. Moreover, generation of noise cannot be avoided, as the printed circuit resin board has a poor shielding effect.
Therefore, to solve this problem a printed circuit board has been constructed in which a resin board and a metal board are glued together by means of a bonding sheet having at least one circuit layer with through holes formed on the resin board and on the metal board. The centers of the through holes are aligned Also offered in U.S. patent application Ser. No. 691,611 now U.S. Pat. No. 4,663,208 is a printed circuit board in which a resin board and a metal board are glued together by way of a bonding sheet having at least one circuit layer through holes are formed on the resin board and holes which are filled with resin are provided on the metal board. Lead wire holes are drilled at the centers of the resin filled holes and the centers of the through holes and those of the lead wire holes respectively are aligned.
In these printed circuit boards, better heat releasing capacity facilitates a higher density of mounted components since there is no deterioration of the mounted components even though the heat generated from the mounted components is greater, and costly mounted components with radiation fins or else are not necessitated. Also their greater flextural rigidity eliminates any chance of cambering by the printed circuit board even if the number of mounted components increases, so that insertion of the printed circuit board into the electronic system can be easily made, and the inserted printed circuit board does not come into contact with neighboring printed circuit boards. Further, this construction yields a better shielding effect for the prevention of noise. Therefore, it is possible to widely expand the applicable scope of printed circuit boards.
The conventional method of manufacturing such printed circuit boards is hereinafter explained. First, circuit layers, through holes and guide holes are formed on a resin board material. At the same time, holes and guide holes are provided on a metal board material which may be filled with resin lead wire holes are drilled through the centers of the resin filled holes. Next, a number of sets of resin board material and metal board material, with a bonding sheet inserted between, are positioned the heat plates of a multilayer press machine, and by heat-pressing them for 1.5 hours at about 170.degree. .C, the resin board material and the metal board material are glued together by means of the bonding sheet. Then, printed circuit boards are made from the set of the resin board material and the metal board material thus glued together after finishing up their outer configurations.
In this type of manufacturing method, however, when gluing the resin board material and the metal board material together by way of the bonding sheet, it has to employ the multilayer press machine which is very expensive, so that the manufacturing cost becomes higher. Also it takes about two hours for heat-bonding the resin board material and the metal board material together by means of the bonding sheet in the multilayer press machine, so that the longer hours required for manufacture reduces its productivity. Further, to manufacture printed circuit boards wherein a metal board is glued only to a part of the resin board, it requires bonding many metal boards to the resin board material, and in this case the operation of bonding the resin board material and metal boards together by way of an inserted bonding sheet is troublesome and takes much time.